Cathode ray tube deflection systems



United States Patent CATHODE RAY TUBE DEFLECTION SYSTEMS Emil E.Sanford, Clfton, N. J., assignor to Allen B.

Du Mont Laboratories, Inc., Clifton, N. J., a corporation of DelawareApplication December 27, 1951, Serial No. 263,621

2 Claims. (Cl. 317-200) The present invention relates to cathode raytube deflection systems and particularly to electromagnetic defiectioncoils for such systems.

It has become standard practice in cathode ray tube picture or imageprojection to form on the cathode ray tube screen, a picture pattern orimage on a raster having an aspect or width to height ratio of 4:3.Heretofore, in systems utilizing electromagnetic coils surrounding theneck of the cathode ray tube for beam deflection, the coil has beenformed in a uniform assembly with perpendicularly displaced polewindings of substantially the same perimetrical dimension. With such anarrangement of pole windings, it has been found that beam spotdistortion adiacent the side or vertically extending edges of the rasteris considerably greater than adjacent the bottom and top or horizontallyextending edges of the raster. Such distortion results in non-uniformresolution of the image throughout the areas adiacent the horizontal andvertical edges and is undesirable.

Accordingly, it is an object of the present invention to provide anelectromagnetic deflection coil with pole windings so arranged as tosubstantially eliminate the non-unifornrity vof resolution of the imagethroughout the edge area of the picture raster of a cathode ray tube.

This and other desirable objects are attained in accordance With thepresent invention by providng an electromagnetic deflection coil withwire sizes and perimetrically distributed pole windings in accordancewith the raster aspect ratio of a cathode ray tube screen.

For a better understanding of the invention, reference may be had to thedrawing in which Fig. 1 is a perspective view with parts broken away ofa deflection coil embodying the present invention and Fig. 2 is aschematic view of the cross-section of the coil of Fig. 1 takensubstantially midway between the axial extremities of the coil.

Referring now to the drawing and particularly to Fig. 1 there isillustrated a cathode ray tube deflection coil or yoke 2 embodying thepresent invention. The yoke comprises two pairs of semi-cylindrical coilwindings 4, 6, 8 and arranged in a unitary cylindrical structure toprovide pole windings of opposite polarity along axes perpendicularlydisplaced. As shown, each of the coil windings 4, 6, 8 and 10 is formedof a plurality of turns of wire with the axially extending portions ofthe coils serving as the pole portions of the windings.

To obtain beam deflection in accordance with the aspect ratio of theconventional cathode ray tube, the size of the wire in the coil windingsand the perimetrical distribution of the pole portions is related to the4:3 aspect ratio of the raster of the standard tube.

To accomplish this end, coils 4 and 6, and 8 and 10 respectively areformed of wire having a size corresponding to the ratio 4:3 and theperimetrical distribution of the pole portions of the respective pairsof coils is likewise in accordance with the ratio 4:3. With therespective coils 4, 6, 8 and 10 formed, coils 4 and 6 are positionedwith the pole portions adjacent each other to form a cylindricalstructure. Thereafter coils 8 and 10 are posi- 2 ,766,407 .'PatentedOct. A9, 1956 ICC vjacent andl fitted in the openings of coils-4 and 6.An

insulating material 12 preferably in the form of a flexible sheet isinterposed between the respective coils 4 and 6, and 8 and 10 to avoidelectrical short circuiting between these coils. With the coil windingsarranged in the positions described, thepole portions of the respectivepairs of windings are centered on axes perpendicularly displaced.

Thereafter the unitary assembly of coils 4, 6, 8 and 10 is surrounded bya second insulating material 14, preferably in the form of a flexiblesheet and a pair of semicylindrical core members 16 of sutable magneticflux conducting material are positioned around the coils to complete theunitary coil structure. To secure the core members .in place, theexternal surface of the core members is wrapped with a continuousadhesive tape 18.

Referring now to Figure 2, there is illustrated the perimetricaldistribution of the pole portions of the coil windings to provideperpendicular fields of magnetic force having cross-sectional areasrelated to the raster aspect ratio. As shown in Figure 2, each of thepole portions of the coil windings 4 and 6 have a perimetricaldistribution corresponding to that portion of a circle intercepted by anangle of 50 degrees. Likewise, each of the pole portions of the coilwindings 8 and 10 have a perimetrical distribution corresponding to thatportion of a circle intercepted by an angle of 37 degrees, 30 minutes.Accordingly, it will be obvious that the perimetrical distribution ofthe pole windings of the respective coils 4 and 6, and 6 and 8 willcorrespond with the raster aspect ratio of 4: 3.

In utilizing the deflection coil of the present invention, the structureis arranged so that the pole portions of greater perimetricaldistribution are aligned on the horizontal axis of the deflection systemof a cathode ray tube and the pole portions of the lesser perimetricaldistribution are aligned along the vertical axis of the system.

With a deflection yoke arrangement such as I have described, the overalltemperature rise and consequent power loss in the yoke is decreased andthe average picture or image definition on a cathode ray tube screen isimproved throughout the horizontal and vertical edge area of the raster.

What I claim as new and desire to Patent of the United States is:

1. A deflection yoke for producing a raster having a given aspect ratio,said yoke comprising a generally hollow cylindrical assembly of fourelectromagnetic coils of wire, each of said coils being wound in arectangular form having four sides and being fitted into saidcylindrical assembly, said assembly comprising pole portions formed bytwo of said sides being straight and substantially parallel to the axisof said cylindrical assembly, and traversed portions formed by theremaning two sides being shaped into arcuate form to define the openingof said hollow cylindrical assembly, said two pole portions and twotraverse portions of each of said coils defining an open portion of eachcoil, said four coils being located around said cylindrical assembly intwo diametrically opposed pairs with the open portions of one of saidpairs being arcuately displaced in said assembly substantially from theopen portions of the other of said pairs, the wire forming the straightsides of one of said pairs of coils lying within and substantiallyfilling the open portions of the other of said pairs, and theperimetrical distribution of the pole portions of one of said pairs ofcoils being greater than the perimetrical distribution of the poleportions of the other of said pairs of coils, the ratio between theperimetrical distribution of the pole portions of said one pair of coilsand the perimetrical distribution of the pole portions of said otherpair of coils being disecure by Letters rectly proportional to saidaspect ratio, the wire size of said one par of coils and the Wire sizeof said other pair of coils having the same relationship as said givenaspect ratio.

2. The deflection yoke according to clairn 1 for use in defiecting anelectron beam over a substantially rectangular area having an aspectratio of 4:3, said poie portions of one of said pairs of coils having aperimetrical distribution ratio With respect to the pole portions of theother of said pairs of 4:3, the Wire size of said first pair of coilshaving a 4:3 ratio to the wire size of said second pair of coils.

References Cited in the iile' of this patent UNITED STATES PATENTSTolson Mar. 23, 1937 Bowman-Manifold Feb. 15, 1938 Blain July 16, 1940Blain Apr. 1, 1941 Torsch Oct. 14, 1947 Thalner Oct. 28, 1952

